Malwarebytes

I've worked with a handful of anti-malware tools before, but the only one that consistently identifies and removes malicious software is Malwarebytes (http://www.malwarebytes.org/).

It's free, though there are paid versions available. You can choose a fast scan (takes about a half an hour) or a full scan (which takes well over an hour).

It has saved my laptop from malicious software several times now (including once this week), and caught malware that other anti-malware programs didn't.

So if your browser has recently began performing slowly, or your home page has mysteriously changed, or your computer has been crashing more often than usual, or you begin seeing excessive pop-up ads (my symptoms this week included pop-up messages NOT from my anti-virus program telling me I'd been infected by malware), give Malwarebytes a try.

A more complete list of symptoms that you've been infected by malware is available at http://www.malwarehelp.org/symptoms-of-infection.html and http://kb.mit.edu/confluence/pages/viewpage.action?pageId=6390681.